时间戳

首页 > 解决方案 > NSSet containsObject 错误结果

ios - NSSet containsObject 错误结果

问题描述

我正在写一个类似于糖果迷恋的游戏。我有一个“交换”类型来表示交换 2 个 cookie。

@interface Cookie : NSObject {

}
@property (strong) Coord2D *coord;
@end
@implementation Cookie {
}

@interface Swap : NSObject {
}

@property (strong) Cookie *cookieA;
@property (strong) Cookie *cookieB;
@end

@implementation Swap
- (BOOL)isEqual:(id)object {
  Swap *other = object;
  return ([_cookieA.coord isEqual:other.cookieA.coord] && [_cookieB.coord isEqual:other.cookieB.coord])
  || ([_cookieA.coord isEqual:other.cookieB.coord] && [_cookieB.coord isEqual:other.cookieA.coord]);
}

- (NSUInteger)hash {
  // (A, B) and (B, A) must be interchangable (hash to the same value)
  return (_cookieA.coord.row + _cookieB.coord.row) ^ (_cookieA.coord.col + _cookieB.coord.col);
}
- (NSString *)description
{
  return [NSString stringWithFormat:@"[%@, %@]", _cookieA.coord, _cookieB.coord];
}

@end

而 the被简单地cookie.coord定义为一个类型Coord2Drowcol

@interface Coord2D : NSObject {
}
@property int row;
@property int col;
@end

@implement Coord2D
- (BOOL)isEqual:(id)object {
  Coord2D *other = object;
  return _row == other.row && _col == other.col;
}

- (NSUInteger)hash {
  return _row ^ _col;
}
- (NSString *)description
{
  return [NSString stringWithFormat:@"(%i, %i)", _row, _col];
}

@end

现在我需要测试一个 NSSet 是否allPossibleSwaps包含一个新创建的swap对象。

(lldb) po allPossibleSwaps
{(
    [(2, 4), (2, 5)],
    [(1, 1), (2, 1)],
    [(1, 0), (2, 0)],
    [(2, 4), (2, 3)],
    [(1, 2), (2, 2)],
    [(0, 4), (1, 4)],
    [(1, 4), (2, 4)],
    [(1, 4), (1, 5)],
    [(2, 3), (2, 4)]
)}

(lldb) po swap
[(1, 4), (2, 4)]

(lldb) p [allPossibleSwaps containsObject:swap]
(bool) $64 = false

结果应该是肯定的，但实际上是否定的。

这里有几个线索：

containsObject: (allObject[6] is wrong!) 同样奇怪的是它们被打印为true/false而不是YES/NO

(lldb) p [allPossibleSwaps containsObject: allPossibleSwaps.allObjects[0]]
(bool) $41 = true
(lldb) p [allPossibleSwaps containsObject: allPossibleSwaps.allObjects[1]]
(bool) $40 = true
(lldb) p [allPossibleSwaps containsObject: allPossibleSwaps.allObjects[2]]
(bool) $42 = true
(lldb) p [allPossibleSwaps containsObject: allPossibleSwaps.allObjects[3]]
(bool) $39 = true
(lldb) p [allPossibleSwaps containsObject: allPossibleSwaps.allObjects[4]]
(bool) $43 = true
(lldb) p [allPossibleSwaps containsObject: allPossibleSwaps.allObjects[5]]
(bool) $44 = true
(lldb) p [allPossibleSwaps containsObject: allPossibleSwaps.allObjects[6]]
(bool) $45 = false
(lldb) p [allPossibleSwaps containsObject: allPossibleSwaps.allObjects[7]]
(bool) $46 = true
(lldb) p [allPossibleSwaps containsObject: allPossibleSwaps.allObjects[8]]
(bool) $47 = true

isEqual 调用（似乎正确）

(lldb) p [(Swap *)(allPossibleSwaps.allObjects[0]) isEqual:swap]
(BOOL) $53 = NO
(lldb) p [(Swap *)(allPossibleSwaps.allObjects[1]) isEqual:swap]
(BOOL) $52 = NO
(lldb) p [(Swap *)(allPossibleSwaps.allObjects[2]) isEqual:swap]
(BOOL) $54 = NO
(lldb) p [(Swap *)(allPossibleSwaps.allObjects[3]) isEqual:swap]
(BOOL) $55 = NO
(lldb) p [(Swap *)(allPossibleSwaps.allObjects[4]) isEqual:swap]
(BOOL) $56 = NO
(lldb) p [(Swap *)(allPossibleSwaps.allObjects[5]) isEqual:swap]
(BOOL) $57 = NO
(lldb) p [(Swap *)(allPossibleSwaps.allObjects[6]) isEqual:swap]
(BOOL) $50 = YES
(lldb) p [(Swap *)(allPossibleSwaps.allObjects[7]) isEqual:swap]
(BOOL) $51 = NO
(lldb) p [(Swap *)(allPossibleSwaps.allObjects[8]) isEqual:swap]
(BOOL) $58 = NO

哈希调用：（似乎正确）

(lldb) p ((Swap *)allPossibleSwaps.allObjects[0]).hash
(NSUInteger) $30 = 13
(lldb) p ((Swap *)allPossibleSwaps.allObjects[1]).hash
(NSUInteger) $31 = 1
(lldb) p ((Swap *)allPossibleSwaps.allObjects[2]).hash
(NSUInteger) $32 = 3
(lldb) p ((Swap *)allPossibleSwaps.allObjects[3]).hash
(NSUInteger) $33 = 3
(lldb) p ((Swap *)allPossibleSwaps.allObjects[4]).hash
(NSUInteger) $34 = 7
(lldb) p ((Swap *)allPossibleSwaps.allObjects[5]).hash
(NSUInteger) $35 = 9
(lldb) p ((Swap *)allPossibleSwaps.allObjects[6]).hash
(NSUInteger) $36 = 11
(lldb) p ((Swap *)allPossibleSwaps.allObjects[7]).hash
(NSUInteger) $37 = 11
(lldb) p ((Swap *)allPossibleSwaps.allObjects[8]).hash
(NSUInteger) $65 = 3
(lldb) p swap.hash
(NSUInteger) $66 = 11

标签： iosobjective-c

解决方案

您的散列和 isEquals 逻辑看起来是正确的。从您的控制台输出判断，哈希值和 isEquals 的行为都符合预期。因此，在重新散列期间，项目很可能被放入错误的桶中。

当您从集合中插入或删除项目时，会发生重新散列。如果您不熟悉散列的工作原理，这里有一篇很好的文章：https ://en.wikipedia.org/wiki/Extendible_hashing

是否有可能您的 cookie 交换逻辑弄乱了集合中已经存在的 Swap 项目？您是否在插入后修改坐标？

推荐阅读